Observations and source investigations of the boundary layer bromine monoxide (BrO) in the Ny-Ålesund Arctic

Abstract

During polar spring, the presence of reactive bromine in the polar boundary layer is considered to be the main cause of ozone depletion and mercury deposition. However, many uncertainties still remain regarding understanding the mechanisms of the chemical process and source of the bromine. As Arctic sea ice has recently been dramatically reduced, it is critical to investigate the mechanisms using more accurate measurements with higher temporal and spatial resolution. In this study, a typical process of enhanced bromine and depleted ozone in the Ny-Ålesund boundary layer in late April 2015 was observed by applying ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) technique. The results showed that there were bromine monoxide (BrO) slant columns as high as 5.6 × 1014 molec cm-2 above the Kings Bay area on 26 April. Meanwhile, the boundary layer ozone and gaseous elemental mercury (GEM) were synchronously reduced by 85 and 90%, respectively. Based on the meteorology, sea ice distribution and air mass history, the sea ice in the Kings Bay area, which emerged for only a very short period of time when the enhanced BrO was observed, was considered to be the major source of this bromine enhancement event. The oxidized GEM may be directly deposited onto snow/ice and thereby influence the polar ecosystem.